This proposal investigates the working hypothesis that phytoremediation can be used to degrade[unreadable] airborne PCB congeners from soil and groundwater sources. Plants stimulate the microbial community[unreadable] in the root zone and contribute to microbial degradation of RGBs (rhizodegradation). Higher-chlorinated[unreadable] PCBs are dechlorinated under reducing (anaerobic) conditions; resulting lesser-chlorinated congeners[unreadable] can undergo oxidative mineralization under aerobic conditions. Alternating reducing and oxidizing[unreadable] conditions in the rhizosphere makes the plant-soil system a natural two-stage bioreactor for initial PCB[unreadable] transformation. Lesser-chlorinated PCBs can also be taken-up and transformed inside plan tissues. The[unreadable] specific aims of the project are (1) to test the hypothesis that poplar plants can take up and detoxify[unreadable] lesser-chlorinated PCB congeners by identifying metabolic pathways of PCBs and genes that encode[unreadable] for catabolic enzymes, (2) to test the hypothesis that bacteria in the rhizosphere can reductively[unreadable] dechlorinate higher-chlorinated PCBs and can mineralize resulting lesser-chlorinated congeners under[unreadable] oxidizing conditions; this will be tested using anaerobic and aerobic batch bioreactors with rhizosphere[unreadable] soils contaminated with PCBs, (3) to test the hypothesis that phytoremediation will allow for significant[unreadable] reductions in the airborne transfer of PCBs from waste disposal sites and mitigate exposure to humans[unreadable] and ecosystems; this innovative cleaning up strategy (based on hypotheses 1 and 2) will be tested at[unreadable] the bench scale and by pot-studies in the greenhouse, (4) to test the hypothesis that residues of PCBs[unreadable] in plant tissues are non-toxic or of greatly reduced toxicity to biota by conducting an eco-toxicological[unreadable] evaluation of the phytoremediation process using a battery of toxicity tests, and (5) to test the[unreadable] hypothesis that higher plants play a significant role in the environmental cycling of airborne PCBs by[unreadable] field analyses of PCB accumulation on vegetation. The significance of this project is that it provides an[unreadable] intervention and remedy for contaminated waste sites that will help to break the continuous cycling of[unreadable] PCBs in the atmosphere and the subsequent exposure to humans.